Replace the 20 year old water heater. It's past its life span. They now make more energy effecient water heaters which will lower your utility bill. Put a blanket around the new water heater while you're at it.
A light period is a menstrual cycle that is shorter and/or lighter than a woman's regular period. Women should familiarize themselves with their menstrual cycle, how many pads or tampons they use, and how long their periods last to quickly detect any changes in their periods.
Light is a transverse electromagnetic wave. In many situations, the wavelengths of the light being studied are very small compared to the dimensions of the equipment used to study the light. Under these conditions we can make an approximation called geometrical optics or ray optics.